@article{f99ba40d42874ebd9f3550c76497ded9,
title = "Deepest View of AGN X-Ray Variability with the 7 Ms Chandra Deep Field-South Survey",
abstract = "We systematically analyze the X-ray variability of active galactic nuclei (AGNs) in the 7 Ms Chandra Deep Field-South survey. On the longest timescale (≈17 years), we find only a weak (if any) dependence of X-ray variability amplitudes on energy bands or obscuration. We use four different power spectral density (PSD) models to fit the anticorrelation between normalized excess variance () and luminosity, and obtain a best-fit power-law index for the low-frequency part of the AGN PSD. We also divide the whole light curves into four epochs in order to inspect the dependence of on these timescales, finding an overall increasing trend. The analysis of these shorter light curves also infers a β of ∼1.3 that is consistent with the above-derived β, which is larger than the frequently assumed value of . We then investigate the evolution of . No definitive conclusion is reached because of limited source statistics, but if present, the observed trend goes in the direction of decreasing AGN variability at fixed luminosity toward high redshifts. We also search for transient events and find six notable candidate events with our considered criteria. Two of them may be a new type of fast transient events, one of which is reported here for the first time. We therefore estimate a rate of fast outbursts and a tidal disruption event (TDE) rate assuming the other four long outbursts to be TDEs.",
author = "Zheng, {X. C.} and Xue, {Y. Q.} and Brandt, {W. N.} and Li, {J. Y.} and M. Paolillo and G. Yang and Zhu, {S. F.} and B. Luo and Sun, {M. Y.} and Hughes, {T. M.} and Bauer, {F. E.} and F. Vito and Wang, {J. X.} and T. Liu and C. Vignali and Shu, {X. W.}",
note = "Funding Information: We thank the referee for careful reading and helpful comments that helped improve the paper. X.C.Z., Y.Q.X., J.Y.L., and M.Y.S. acknowledge the support from the 973 Program (2015CB857004), the National Natural Science Foundation of China (NSFC-11473026, 11421303), the CAS Frontier Science Key Research Program (QYZDJ-SSW-SLH006), and the Fundamental Research Funds for the Central Universities. B.L. acknowledges support from the National Natural Science Foundation of China grant 11673010 and the Ministry of Science and Technology of China grant 2016YFA0400702. T.M.H. acknowledges the CONICYT/ ALMA funding Program in Astronomy/PCI Project N°:31140020. T.M.H. also acknowledges the support from the Chinese Academy of Sciences (CAS) and the National Commission for Scientific and Technological Research of Chile (CONICYT) through a CAS-CONICYT Joint Postdoctoral Fellowship administered by the CAS South America Center for Astronomy (CASSACA) in Santiago, Chile. F.E.B. acknowledges support from CONICYT-Chile (Basal-CATA PFB-06/2007, FONDECYT Regular 1141218), the Ministry of Economy, Development, and Tourism{\textquoteright}s Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS. Publisher Copyright: {\textcopyright} 2017. The American Astronomical Society. All rights reserved..",
year = "2017",
month = nov,
day = "10",
doi = "10.3847/1538-4357/aa9378",
language = "English (US)",
volume = "849",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2",
}